Vitamin C and Phenolic Compound Concentrations in the Leafy Vegetables Solanum scabrum and Gynandropsis gynandra

Leafy vegetables are an important source of vitamins, phenolic compounds, and various health-beneficial compounds such as minerals and carotenoids. Solanum scabrum and Gynandropsis gynandra are leafy vegetables that are consumed in rural areas around the world as a main food, food ingredient, or traditional medicine. Currently, there is limited information about their nutritional and bioactive composition. Therefore, the goal of this research was to evaluate the concentration of vitamin C (reduced, oxidized and total), and phenolic compounds (free, bound, and total) in the leaves of two accessions of S. scabrum and eight accessions of G. gynandra. Seeds were obtained from the USDA National Plant Germplasm System (Columbus, OH).  Plants were grown in synthetic soil in an environmental growth chamber for five weeks. Plants of each accession were grown in triplicate. Vitamin C and phenolic compounds were quantified using spectrophotometric methods. Results are normalized per gram fresh weight (g FW). The concentration of total vitamin C in these leaves was from 0.94 to 1.40 mg ascorbic acid (AA)/g FW. The highest concentrations of total vitamin C were found in G. gynandra PI 500650 (1.40 ± 0.08 mg AA/g FW), G. gynandra PI 490299 (1.34 ± 0.07 mg AA/g FW) and S. scabrum PI 643126 (1.28±0.09 mg AA/g FW). On the other hand, the total phenolic compound concentrations were from 2.29 to 4.42 mg gallic acid equivalents (GAE)/g FW, with free phenolic compounds predominating (43% to 81% of total).  Gynandropsis gynandra PI 500650 (4.42 ± 0.32 mg GAE/g FW) had the highest concentration of total phenolic compounds, followed by S. scabrum Grif 14198 (3.42 ± 0.45 mg GAE/g FW) and G. gynandra PI 500677 (3.28 ± 0.32 mg GAE/g FW).  A serving size (1 cup: 30 g FW) of these leafy vegetables contains from 28 to 42 mg AA.  By comparison, a one cup serving of a fresh leafy vegetable like spinach, mustard greens or collard greens has 8.4, 21, or 10.6 mg AA, respectively (according to the USDA National Nutrient Database for Standard Reference).  Additionally, a single serving of G. gynandra PI 500650 or G. gynandra PI 490299 would contribute approximately 67% of the daily value (DV) of vitamin C  (DV = 60 mg; as established by the U.S. Food and Drug Administration).